P&I Urges Use of Parallel Indexing

Friday, September 01, 2006

The London P&I Club has said that two recent casualties may well have been avoided if the bridge teams of the vessels involved had made use of parallel indexing, a radar technique which can enable navigators to monitor continuously for cross track error. Writing in the latest issue of its StopLoss Bulletin, the Club says, “In one case, a bulk carrier was passing close by the edge of a busy anchorage while preparing to pick up a pilot. The master had approved a comprehensive berth-to-berth passage plan which confirmed that the ship would be subject to a strong, cross tidal stream on the last leg from the anchorage to the pilot station, and also identified an appropriate parallel index.
“But the bridge team failed to set up the parallel index on the radar, and also failed to fix the ship’s position with sufficient frequency. The helmsman had been told to steer for a clearly visible landmark, but no-one realized that, while the helmsman had kept the foremast aligned with the landmark, the compass course was changing steadily as the ship was set off the intended track. The master had become distracted and, by the time he noticed the danger, it was too late to avoid a collision with an anchored vessel.”
The second case highlighted by the Club involved a feeder containership which, during an approach to an inner anchorage, was required to pass relatively close to a charted coral reef. In this case, the ship had no formal passage plan and the master was unaware that a strong current ran across the intended track.
Although the end of the breakwater provided an obvious target for use in a simple parallel index, no use was made of it. And that omission had been compounded by fixing only by GPS and at insufficiently frequent intervals. As a result, the master only became aware that he was off track when the ship grounded heavily, causing damage to the reef.
The Club says, “Both these casualties illustrate the value of parallel indexing, in addition to the proper fixing of a ship’s position at appropriate intervals. In particular, parallel indexing provides ‘real time’ monitoring for cross track error between fixes, in that the radar target can be seen moving off the index line if the ship deviates from the track.
“And the use of the technique in these two cases should have given the bridge teams early warning that their ships were running into danger.”